In the field of an organic thin film transistor device, an organic thin film solar cell, an organic EL display and the like, many functional thin films are investigated. The functional thin film is a thin film subjected to so-called fine patterning, which includes a material exhibiting various functions and is arranged at locations where the functions needs to be exhibited in a device with precision required for exhibiting the functions. Examples of the functions to be exhibited by patterning include functions of wiring, an electrode, an insulating layer, a light-emitting layer, a charge transporting layer and the like. As a technique of performing such patterning, there is, for example, a photolithography method. That is, a method for forming a functional thin film in which a thin film is formed over a surface of a substrate and the like, a layer containing a photoresist material is then formed on the thin film, and the thin film is finely patterned with the use of photosensitivity of the photoresist material. However, the functional thin film prepared with the photolithography method is likely to deteriorate highly in various functions since the steps such as UV irradiation, developing, washing and the like on the photolithography method are performed. Particularly, when the functional thin film is a functional organic thin film, functions of the functional organic thin film are likely to be highly damaged with performing the steps such as developing and washing.
As a method for solving the problem of a photolithography method, it has been proposed a method that a functional thin film is directly patterned on a substrate by using an ink-jet method, a nozzle coating method, and various roll printing methods, for example, a flexo printing or reversing. These printing methods use an ink which is usually relatively low in concentration and viscosity. Therefore, there are such methods for precisely forming a functional thin film at only the required position that a partition wall for preventing the ink from flowing is formed in a region surrounding the region where the functional thin film is formed, and that a lyophilic region which can accept the ink and a liquid-repellent region which do not accept the ink are formed on a surface of a substrate.
As the method in which a lyophilic region and a liquid-repellent region are formed on a surface of a substrate, there is known a method in which a liquid-repellent substance such as a fluorine-containing silane coupling agent is applied onto a surface of a lyophilic thin film to form a liquid-repellent thin film, a part of the liquid-repellent thin film is irradiated with light having a wavelength less than 200 nm to decompose the liquid-repellent substance, and then the decomposed product is removed. In the substrate obtained by this method, only a site irradiated with light becomes a lyophilic surface (Patent Document 1).
Further, as a method of using light having a wavelength of relatively long wavelength, there is a method in which a thin film of a liquid-repellent composition, containing a compound having a liquid-repellent group and a photopolymerization initiator, is formed on a lyophilic substrate, and a part of the thin film is irradiated with light to polymerize the liquid-repellent composition and make the composition insoluble in a solvent, and an unpolymerized portion of the composition is removed by use of a solvent to pattern a lyophilic region (Patent Document 2).
Moreover, as a method of using ultraviolet light with a relatively long wavelength, there is also known a method in which a liquid-repellent thin film containing a photocatalyst such as titanium oxide is formed on a lyophilic layer and a part of the thin film is irradiated with light to decompose the liquid-repellent thin film and to pattern a lyophilic region (Patent Document 3).